1. Field of the Invention
The present invention relates to a thermoplastic polymer composition and, more specifically, to a thermoplastic polymer composition comprising a thermoplastic polymer having polarity on the main chain thereof and a modified block copolymer to which a carboxylic acid group or derivatives thereof has added, the composition having excellent mechanical characteristics with the two components having improved compatibility.
2. Description of the Related Art
Polymeric substances have been widely used as materials for fibers, films, sheets and like shaped articles, and it sometimes happens that these substances, when used alone, do not sufficiently meet the intended purpose. A variety of attempts have therefore been made to combine a polymeric substance with other components to form compositions or laminates, thereby providing the resulting products with sufficient strength, improved processability, reduced cost or like advantages. However, different types of polymeric substances, when combined together to form a composition, seldom have good compatibility with each other. As a result, most of compositions comprising different types of polymeric substances with poor compatibility have problems in achieving the intended improvements due to non-uniformity, inter-layer delamination between the different polymer layers or like troubles resulting from the poor compatibility.
It is known, in order to obtain compositions having good properties by blending different polymeric substances, to use as one component a block copolymer comprising a polystyrene block and a polybutadiene block, one comprising a polystyrene block and a polyisoprene block, or a hydrogenated block copolymer obtained by partially hydrogenating the foregoing (for example, Japanese Patent Application Laid-open Nos. 119055/1975, 148457/1975, 75651/1975, 117940/1977 and 150457/1977). However, these block copolymers cannot be said to be useful for improving the characteristics of thermoplastic polymers having polarity on their main chain, such as polyamides, thermoplastic polyesters and thermoplastic polyurethanes, because of markedly poor compatibility with these polymers.
There are known compositions capable of modifying polyamides, thermoplastic polyesters, thermoplastic polyurethanes and the like, incorporating into these thermoplastic polymers a block copolymer obtained by permitting a carboxylic acid or derivatives thereof to add to a partially hydrogenated product of a block copolymer comprising an aromatic vinyl compound polymer block and a conjugated diene compound polymer block (for example, U.S. Pat. Nos. 4,174,358, 4,628,072, 4,659,970, 4,820,768 and 4,972,020). However, although these compositions, with an improved compatibility of the thermoplastic polymers with themselves, exhibit relatively better mechanical properties, they have poor resistance to shock at low temperatures and have some problem with respect to oil resistance.
There are compositions incorporating a thermoplastic polymer such as polyamides, polyethylene terephthalate or polybutylene terephthalate and a block copolymer obtained by permitting a carboxylic acid or derivatives thereof to add to a partially hydrogenated product of a block copolymer having a structure of X--Y--X or X--Y--X--Y, wherein X and Y represent a polybutadiene block having a degree of vinylization of not more than 20% and one having a degree of vinylization of 30 to 95%, respectively (Japanese Patent Application Laid-open No. 74409/1991). The compositions still have the drawback of poor impact strength at low temperatures, while eliminating the problem of poor oil resistance though.